1. Field of the Invention
The present invention relates to fixing roller for fixing unit, fixing unit, image forming apparatus, roller replacement aid for fixing unit, and method of replacing fixing roller in fixing unit.
2. Description of the Related Art
A known fixing unit for an image forming apparatus such as a laser beam printer or a copying machine, conveys a recording medium carrying a toner image, which is not yet fixed on a surface thereof, while being nipped between a heating roller and a pressing roller to apply heat and pressure and fixes the toner image onto the recording medium.
A plurality of heater lamps as heat sources is arranged inside the heating roller. Generally, an image forming apparatus that provides higher printing speed or that supports larger ream weight requires larger thermal capacity for fixing of toner images. In such an apparatus, it is necessary to keep the heating roller at a certain temperature or higher. This results in an increase in fixing temperature.
When such a heating roller that has kept at high temperature ends its life and is to be replaced, the operation performed by the image forming apparatus must be stopped, and the heating roller must be then cooled down to a temperature at which it can be replaced. Subsequently, a servicing engineer removes the heating roller from the fixing unit to replace the heating roller with a new one. Because the heating roller requires a long time to cool down, the replacement task is very inefficient. Furthermore, because the image forming apparatus is kept out of service over an extended time period, not only the productivity of the image forming apparatus is reduced but also the cost for replacement and maintenance tasks would be high.
In recent years, because an image forming apparatus is required to provide high speed printing, to achieve high image quality, and to support different types of paper, different types of heating rollers need to be incorporated in the fixing unit. For high speed printing, a heating roller with a surface layer coated by a thin coat of tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA) resin is used to speed up supply of heat required for fixing toner images. For high image quality, a heating roller with a surface layer covered by silicone rubber, for example, is used to minimize smudge or bleeding during fixing of toner images. When durability of the heating roller is required while keeping a certain level of image quality, a heating roller with a silicone rubber layer covered by a PFA tube, for example, is used.
To satisfy such needs with a single image forming apparatus, a heating roller must be replaced with one that fits the need. The heating roller basically has a large thermal capacity while there are some differences depending on types of heating rollers, and it takes quite a long time for the heating roller, which has been kept at a high-temperature for supplying a heat amount required to optimally fix toner images, to cool down so that the heating roller can be replaced.
Japanese Patent Application Laid-open No. H5-504633 discloses an example of how a heating roller is replaced. FIG. 24 is a partial sectional view of a fixing unit disclosed in Japanese Patent Application Laid-open No. H5-504633, and FIG. 25 is a perspective view of the fixing unit with a heating roller included therein being replaced.
As illustrated in FIG. 24, one end of this heating roller 100 is supported by a frame 102 via a supporting flange 101. The supporting flange 101 has a shaft bearing 103. The shaft bearing 103 and a centering member 104 are fitted into an opening end of the heating roller 100. The other end of the heating roller 100 is similarly supported by a supporting flange via a shaft bearing, although not illustrated.
The supporting flange 101 is fixed to the frame 102 by way of a thumbscrew 106. A holding claw 108 is fixed in the supporting flange 101 via a thumbscrew 107. The holding claw 108 functions to fix the heating roller 100 while the heating roller 100 is being replaced.
A plurality of radiator modules 105 is arranged inside the heating roller 100. One end of each of the radiator modules 105 is held at the center of the supporting flange 101 via a holding member 109. Although not illustrated, the other end of each of the radiator modules 105 is similarly held on the supporting flange indirectly via a holding member.
As illustrated in FIG. 24, a connector 110 provided to an end of each of the radiator modules 105 protrudes from the supporting flange 101 with the radiator modules 105 being held at the center of the supporting flange 101. A grip 111 for replacing the heating roller 100 is integrated with the supporting flange 101. The grip 111 is arranged so as to straddle the connector 110 provided to the radiator modules 105 protruding from the supporting flange 101.
To replace the heating roller 100, the thumbscrew 106 is loosened, and the heating roller 100 is pulled out of the frame 102 together with the supporting flange 101 and other components by holding the grip 111 with one hand as illustrated in FIG. 25. Felt 130 is pasted on the outer circumference of the opening of the frame 102 to prevent the heating roller 100 from being damaged because of contact with the frame 102 upon passing through the opening of the frame 102.
The heating roller used in this type of fixing unit is cylindrical in shape, with a diameter of approximately 100 millimeters and a length of 500 millimeters or longer, and is quite heavy. Under such conditions, in the fixing unit disclosed in Japanese Patent Application Laid-open No. H5-504633, inserting and removing operations could be unstable due to the weight and the heat of the heating roller 100 and other components when the heating roller 100 is pulled out together with the supporting flange 101 and the like from the frame 102 by holding the grip 111 with one hand and supporting the heating roller 100 with the other hand wearing a glove 120. The surface of the heating roller 100 may be damaged as a result of coming in contact with other components such as the frame 102 while the heating roller 100 is being replaced.
Because positioning of the heating roller 100 is unstable and no aid is available to stabilize the positioning of the heating roller 100, the heating roller 100 is supported with a hand wearing the glove 120 during the replacement in an embodiment disclosed in Japanese Patent Application Laid-open No. H5-504633. However, there is some operability problems in that, for example, the hand could get burnt if it touches the heating roller 100 in a high-temperature condition, or parting agent or lubricant attached on the heating roller 100 could smear the glove 120.
In addition, because the roller surface may be damaged as a result of the heating roller 100 coming in contact with the frame 102 while being pulled out together with the supporting flange 101 and other components from the frame 102 by holding the grip 111 with one hand, the felt 130 is pasted around the opening of the frame 102 to protect against the damage. However, swear could be accumulated on the felt 130 because the heating roller 100 with parting agent or lubricant attached is slid over the felt 130. Therefore, the felt 130 is insufficient as a protection of the surface on the heating roller 100.
Furthermore, because the felt 130 must be pasted or peeled off every time the heating roller 100 is replaced, the replacement operation becomes cumbersome. Moreover, because the felt 130 becomes dirty every time the heating roller 100 is replaced, it is necessary to discard the dirty felt 130 and get new felt 130 ready.